This invention relates to cast structures, such as pavements, foundations, floors, ceilings, containments, doors, railway ties, roofs, skylights, walls, and to reinforcement and maintenance of the same.
Many composite materials are made of two components: a continuous phase component and a reinforcing component. The continuous phase component is typically a cast material such as asphalt, cement, concrete, ceramic, or glass, or combinations thereof. These materials have good compressive strength, but typically lack flexural and tensile strength. The reinforcing component is a strong material having good tensile strength, such as graphite fiber, polyamide fiber, or steel. Common examples of such composites in civil structures are steel-reinforced concrete and asphalt or concrete reinforced with polymeric grids or weaves.
The primary purpose of reinforcing components is to enhance the capability of a composite to withstand tensile and flexural stresses, particularly after cracks have formed in the continuous phase component. Some prior art composites have included random length and randomly oriented hollow fibers as reinforcing members. For example, pyrolytic graphite fibers having a lumens a few nanometers in diameter have been used to reinforce ceramics and plastics. Straw, which has little tensile or flexural strength, and has a lumens about 2 mm in diameter, has been used to make ceramic bricks and has been mixed into cement for many years. Such hollow reinforcement materials have proved to be useful, but have no utility beyond adding dimensional stability or limited tensile strength to the composite materials in which they are used.
Conduits have been cast into continuous phase materials. For example, thin-walled heating conduit has been cast into pavements for the purpose of deicing. However, such pavement usually also contains solid steel rebar to provide tensile strength. The heat pipe is quite flexible and thus does not provide significant flexural or tensile strength reinforcement. Smooth-walled conduit has also been cast into concrete structures to receive electrical wiring. The smooth outer surface texture of such pipe and conduit does not permit mechanical interlock with the surrounding concrete, and so provides negligible tensile and flexural reinforcement to the concrete.
There is also a procedure for concrete reinforcement that is known as "post tensioning." According to this procedure, very thin-walled (less than 2 mm) conduits having only slightly greater tensile and flexural strength than concrete are cast into concrete structures and cables run through the conduits. After the concrete has cured, the cables are tensioned and a grout injected to mechanically interlock the cable to the composite. This imparts a compressive stress to the composite to oppose tensile stresses that develop in service.
While all of the above-mentioned technologies are highly useful, they do not make the most efficient use of materials for the reinforcement of cast structures.